Haskell:System.Environment
lastmod 2020-09-27created 2020-09-274 edits
Miscellaneous information about the system environment.
Synopsis
getArgs :: IO [String]
getProgName :: IO String
getExecutablePath :: IO FilePath
getEnv :: String -> IO String
lookupEnv :: String -> IO (Maybe String)
setEnv :: String -> String -> IO ()
unsetEnv :: String -> IO ()
withArgs :: [String] -> IO a -> IO a
withProgName :: String -> IO a -> IO a
getEnvironment :: IO [(String, String)]
lookupEnv
Returns the value of the environment variable var, or Nothing if there is no such value.
For POSIX users, this is equivalent to #getEnv.
Since: 4.6.0.0
Example
import System.Environment
main = do
setEnv "FOO" "1"
putStr "FOO:" >> (putStrLn =<< getEnv "FOO")
putStr "BAR:" >> (print =<< lookupEnv "BAR")
putStrLn ""
mapM_ putStrLn =<< map fst `fmap` getEnvironment